Solid oxide fuel cells (“SOFC's”) are solid-state devices which use an oxygen ion conducting ceramic electrolyte to produce electrical current by transferring oxygen ions from an oxidizing gas stream at the cathode of the fuel cell to a reducing gas stream at the anode of the fuel cell. The oxidizing flow is typically air, while the fuel flow can be a hydrocarbon fuel, such as methane, natural gas, pentane, ethanol, or methanol. The fuel cell, operating at a typical temperature between 750° C. and 950° C., enables the transport of negatively charged oxygen ions from the cathode flow stream to the anode flow stream, where the ion combines with either free hydrogen or hydrogen in a hydrocarbon molecule to form water vapor and/or with carbon monoxide to form carbon dioxide. The excess electrons from the negatively charged ion are routed back to the cathode side of the fuel cell through an electrical circuit completed between anode and cathode, resulting in an electrical current flow through the circuit. This type of fuel cell is seen as especially promising in the area of distributed stationary power generation.
Fuel cell stacks are frequently built from a multiplicity of cells in the form of planar elements, tubes, or other geometries. Fuel cell stacks, particularly those with planar geometry, often use seals between electrolyte and interconnect surfaces to contain fuel and air at various locations within the stack. The stacks are often internally manifolded for fuel and/or air flow, and the ceramic electrolyte material can include internal openings or holes to accommodate fluid flow within the stack.
Cracks in the ceramic electrolyte used in solid oxide fuel cells are a primary cause of failure of these devices. The fuel riser openings, which may be circular holes, cause stress concentrations in the ceramic electrolyte and many cracks are found in the vicinity of these openings. Currently, fuel cell stacks undergo an elaborate inspection process including electrical measurements as well as visual inspections to detect cracks as early as possible in the manufacturing process and to eliminate defective cells.
The current inspection processes for detecting cracks in the electrolyte are time-consuming and labor-intensive and often fail to adequately detect cracks. An undetected crack can result in catastrophic failure of the fuel cell stack. There is therefore a need for improvements in the detection of cracks in ceramic electrolyte material.